Currently the demand for polyethylene worldwide is in excess of 80 million metric tons per year. Because there is a need for significant and continued differentiation of polymer products in the polyethylene business, researchers have devoted a great deal of effort to searching for process alterations that will yield such new products. One focus involves exploring new catalysts.
Conventional solution polyethylene Ziegler Natta catalysts based on a Ti precursor supported on precipitated MgCl2 yield linear low density polyethylene (LLDPE) resins with broad molecular weight distributions and composition distributions.
In LLDPE production, ethylene is generally copolymerized with a short-chain olefin comonomer (for example, 1-butene, 1-hexene and/or 1-octene). The resulting polymer is substantially linear but includes significant numbers of short chain branches, and these characteristics give it a higher tensile strength, higher impact strength and higher puncture resistance than those of low density polyethylene (LDPE). LLDPE is used predominantly in film applications due to its toughness, flexibility and relative transparency. Product examples range from agricultural films, food protection wrap, and bubble wrap, to multilayer and composite films.
Polyethylene resins with narrowed molecular weight distributions (MWDs) provide enhanced film properties useful in food and specialty packaging (F&SP) applications. Specifically, a combination of good properties related to dart drop impact, 45 degree gloss, and haze are desirable for F&SP films.